This invention relates to a novel prepolymer and a method for preparation thereof and, more particularly, to a novel prepolymer and a method for preparation thereof, which prepolymer has a styryl group rich in polymerizability and addition reactivity in its side chain and an alkylene sulfide group in its main chain superior in optical properties, such as refractive index and color aberration, mechanical and thermal properties, such as resistance against warping, shock-proofness or thermal stability and chemical stability such as weatherability or resistance against solvents and which may be utilized for a high molecular material such as optical resins, e.g. plastic lenses or anti-refraction coating, coating resins or ornamental resins or high molecular material modifiers. The present invention also relates to a polymerizable composition utilizable as a polymerization component such as an optical resin, a coating resin or an ornamental resin and an optical material utilizable as plastic lenses for eye-glasses or business machines.
As prepolymers having double bonds, there have hitherto been known unsaturated polyesters, which are condensates of maleic anhydride, phthalic acid and ethylene glycol, oil-modified alkyd resins, which are condensates of phthalic acid, glycerin and oleic acid, or oligoester acrylates, which are condensates of polyethylene glycol and acrylic acid. The resins produced by cross-linking these prepolymers are known to be superior in mechanical properties and resistance against solvents by the three-dimensional structure of the resins, while being free from generation of by-products during curing and being curable with a minor quantity of catalysts.
There is proposed in Japanese Laid-open Patent Application No. 2-160762 dimercaptodiphenyl sulfide dimethacrylate, while there is disclosed in Japanese Laid-open Patent Application No. 2-29401 a sulfur-containing polymerizable monomer, such as 2-(vinyl benzyl sulfide) benzothiazole. However, a prepolymer having an alkylene sulfide group in its main chain and a reactive styryl group in its side chain has not been known to data.
Recently, synthetic resin materials excellent in lightness in weight, moldability, shock-proofness and dyeability, are being used as plastic lens materials to take the place of inorganic glass. These synthetic resin materials may be enumerated by, for example, polymethyl methacrylate, polydiethylene glycol bisallyl carbonate, polystyrene and polycarbonate. Polymethyl methacrylate and polydiethylene glycol bisallyl carbonate, however, are as low as about 1.49 in refractive index, although they are superior in lightness in weight and shock-proofness, such that, if these resin materials are employed for lenses, it becomes necessary to increase the lens thickness as compared to that of a lens of inorganic glass, and hence these resin materials are not suited for use for high multiplication or lightweight lenses. On the other hand, while polystyrene and polycarbonate are as high as 1.58 to 1.59 in refractive index, they are thermoplastic resins and hence are susceptible to optical distortion due to double refraction in the course of injection molding, while being inferior in resistance against solvents or scratch-proofness.
Recently, a variety of proposals have been made for obviating these drawbacks. For example, there is disclosed in Japanese Laid-open Patent Application No. 53-7787 a copolymer of diethylene glycol biscarbonate and diallyl isophthalate, while there are disclosed in Japanese Laid-open Patent Application Nos. 59-81318 and 59-191708 a copolymer of diallyl phthalate and an unsaturated fatty acid alcohol--benzoic acid ester and a copolymer of a di(meth)acrylate having bisphenol A, diallyl isophthalate and diethylene glycol bisallyl carbonate, respectively. While these copolymers have the refractive index on the order of 1.52 to 1.55, these copolymers are defective in that unreacted allyl monomers tend to be left.
On the other hand, there are disclosed in Japanese Laid-open Patent Application Nos. 57-28115 and 60-55007 a copolymer of styrene vinyl monomer and heavy metal salts of unsaturated carboxylic acid and a copolymer of halogen-substituted diallyl phthalate and halogen-substituted allyl benzoate, respectively. While these copolymers are as high as about 1.58 to 1.60 in refractive index, these copolymers are defective in that the specific gravity of the copolymers is high since the allyl monomer having a halogen-substituted aromatic ring or metal salts is employed, and hence the resulting lens cannot be reduced in weight.
In addition, there are proposed in Japanese Laid-open Patent Application Nos. 2-160762 and 2-29401 dimercapto diphenyl sulfido dimethacrylate and 2-(vinyl benzyl sulfide) benzothiazole, respectively as mentioned above. Although these polymers are as high as about 1.60 to 1.70 in refractive index, these polymers exhibit color aberration and are inferior in dimensional stability, while the polymerization reaction thereof is difficult to control. In addition, these polymers are high in specific gravity and inferior in weatherability.